EGR valve opening too soon

[carmangary]

I am pretty sure my EGR valve is opening too soon. The EGR valve is OK because the same problem occurs with a known good one. If I just touch the accelerator it stumbles just enough to be noticable. If I plug the hose to the EGR valve the problem goes away. What could make an EGR valve open too soon? The shop manual suggests checking the intake manifold passages. I'll try that this weekend. Any other thoughts or suggestions?

 

[Bonnewagon]

Most GM EGR valves are of the backpressure actuated type. This means that unless there is sufficient exhaust backpressure to close a port in the valve, it won't operate. Do you have a restricted exhaust system that would show too much backpressure? Also hook up a vacuum gauge to the port you are using for the EGR. It should be ported vacuum that increases as the throttle is opened. It will show 0" at idle. If you are using a full manifold port, it will have high vacuum all the time and try to operate the EGR. It won't open at idle, but as soon as the backpressure builds up, it will.

 

[mickey-d]

Don't they also work off a water temp activated vacuum source? Seems to me there is a vacuum operated, heat sensitive valve with several vacuum ports for different uses. Full manifold vacuum to the valve then heat opens the chambers to metered vacuum. Yes/no? .................mickey-d :lol:

 

[carmangary]

Mine is just the simple type. It comes off ported vacuum through a TCV valve thing that is inline with the vacuum hose. The TCV is supposed to be closed below 61F for cold mornings. So, that can't be it since the temps are in the 70s/80s now.

Exhaust pressure should be fine. I just put on a new cat and the bumper is relatively new, too.

I'll double check the vacuum source and I am going to clean the injector tubes under the carb.

 

[carmangary]

I pulled the EGR and carb today. Despite what the shop manual says, there are no "EGR injector tubes" under my carburetor. But there is a big plug with a 1/2 socket hole in it. It took a big breaker bar to get the plug out and there was a bunch of carbon under it. It wasn't too bad actually, but I cleaned it out to get rid of what was there.

I noticed when I removed the carb that the hot air pipe was not connected to the choke. I forgot to connect it the last time I put the carb back on. So, I made sure to hook it up this time. The car seems to run better now but I'll have to drive it some more to be sure.